Meet-URO12 was a randomized phase 2 trial testing the poly-ADP ribose-polymerase (PARP) inhibitor niraparib as maintenance treatment in patients with advanced urothelial cancer after platinum-based chemotherapy. We did not demonstrate a significant improvement in progression-free survival. The conduction of a phase 3 trial with single agent niraparib in this population is not supported by these results. Platinum-based chemotherapy (PBCT) is the standard first-line treatment for advanced urothelial carcinoma (UC). Potential cross-sensitivity can be hypothesized between platinum drugs and poly-ADP ribose-polymerase (PARP) inhibitors. To compare maintenance treatment with the PARP inhibitor niraparib plus best supportive care (BSC) versus BSC alone in patients with advanced UC without disease progression after first-line PBCT. Meet-URO12 is a randomized, multicenter, open-label phase 2 trial. Patients with advanced UC, without disease progression after four to six cycles of PBCT, with Eastern Cooperative Oncology Group (ECOG) performance status 0 or 1, were enrolled between August 2019 and March 2021. Randomization was stratified by ECOG performance status (0/1) and response to PBCT (objective response/stable disease). Patients were randomized (2:1) to experimental arm A (niraparib 300 or 200 mg daily according to body weight and baseline platelets, plus BSC) or control arm B (BSC alone). The primary endpoint was progression-free survival (PFS). The analysis was performed on an intention-to-treat basis. The secondary endpoints reported in this primary analysis are progression-free rate at 6 mo and safety (adverse event rate). Fifty-eight patients were randomized (39 in arm A and 19 in arm B). The median age was 69 yr, ECOG performance status was 0 in 66% and 1 in 34%; and the best response with chemotherapy was objective response in 55% and stable disease in 45%. The median PFS was 2.1 mo in arm A and 2.4 mo in arm B (hazard ratio 0.92; 95% confidence interval 0.49–1.75, p = 0.81). The 6-mo progression-free rates were 28.2% and 26.3%, respectively. The most common adverse events with niraparib were anemia (50%, grade G3 11%), thrombocytopenia (37%, G3–4 16%), neutropenia (21%, G3 5%), fatigue (32%, G3 16%), constipation (32%, G3 3%), mucositis (13%, G3 3%), and nausea (13%, G3 3%). The main limitation of the study is the small sample size: in March 2021, approval of maintenance avelumab for the same setting rendered randomization of patients in the control arm to BSC alone unethical, and accrual was stopped prematurely. Addition of maintenance niraparib to BSC after first-line PBCT did not demonstrate a significant improvement in PFS in patients with UC. These results do not support the conduction of a phase 3 trial with single agent niraparib in this population. In this trial, we tested the efficacy of niraparib as maintenance treatment in patients affected by advanced urothelial cancer after the completion of first-line chemotherapy. We could not demonstrate a significant improvement in progression-free survival with maintenance niraparib.